Apparatus for fusion electrolysis of reactive metals



Oct. 25, 1960 R. M. SARLA ET AL APPARATUS FOR FUSION ELECTROLYSIS OFREACTIVE METALS Filed Feb. 20, 1958 2 Sheets-Sheet 1 Depsi1ed` Material"aan IN VEN TORS RALPH M. SARLA ERNST O. SCHNEIDERSMANN TTOR EV Oct.2K5, y1960 R. M. sARLA ETAL 2,957,816

APPARATUS P0P FUSION ELECTROLYSIS oF REACTIVE METALS Filed Feb. 20, 19582 Sheets-Sheet 2 INVENToRs A' RALPH M. sARLA alg ERNST o. scHNElDERsMANN19V/MAJ- le 07%,.

ATTORNV APPARATUS FOR FUSIN ELECTROLYSIS OF REACTIVE METALS Ralph M.Sarla, Ramsey, NJ., and Ernst O. Schneidersmann, Wanne-Eickel, Germany,assignors to Union Carbide Corporation, a corporation ofNew York FiledFeb. 20, 1958, Ser. No. 716,322

v 6 Claims. (Cl. 204--225) ThisV invention relates to a high-temperaturecell for the-fusion electrolysis of the high meltin-g point reactivemetals of groups IV, V and VI of the periodic table. More specifically,the invention is concerned with a cell for the electrolysis of thehalides of such reactive metals in a fused salt bath consisting ofalkali or alkaline earth metal halides.

\ Reactive metals of groups IV, V and VI of the periodic table are pronevto embrittlement if contacted withair at the hightemperatures at whichtheir fusion electrolysis production is conducted. The inherentsusceptibility of these metals to contamination by oxygen and nitrogen,particularly,` requires `that certain measures be taken to protect thesemetals .when they are still in their pure, newly deposited,` form.

The most successful measure instituted to maintain the purity of thedeposited reactive metal is to perform the electrolysis `under vacuum orunder the protective shield of an inert gas. Although this method ofpresent-day practice is entirely successful, removal of the cathode onywhich the metal is depositedin the fused salt bath is eventuallynecessary, entailing interruption of the entreprocess'. The reactivemetal deposit, once withdrawn, must then' be allowed to cool, since itsexposure to the atmosphere in its hot condition would quickly negate thepurity protection afforded it Within the shielding enclosure of thecell. This cooling period, however, is sufficiently long to allowsolidiiication of the salt bath, which must then be remelted for thenext operation. A batch-type operation of this nature increases the costof the metal considerably and represents an extremely ineflicient methodof production, for the cell is idle almost as long as it is productive.

The high temperatures necessary in Ithe fusion electrolysis of therefractory metal halides, and the readiness of the pure metals to reactin the atmosphere have, until now, prevented the development of acontinuous or semicontinuous method for removal of the cathode products.7 With a View to overcoming such prior art shortcomings, it is an objectof this invention to provide an electrolytic cell which is compatiblewith a practically continuous production of high melting point reactivemetals by fusion electrolysis.

A further object of the invention is -to provide an electrolytic cellwhich operates under conditions which exclude air or moisture Iatelevated temperatures, is simple to control, and is capable ofcontinuously producing reactive metals of high purity.

, These and other objects and advantages are achieved by theincorporation in an electrolytic cell of -an assembly having a pluralityof cathodes which can be shifted from side to side over the cellentrance while maintaining an eifective gas tight seal.

l Referring now to the attached drawings,

Fig. 1 illustrates, in cross section, the lapparatus of the invention.

Fig. 2 is an enlarged sectional side view of the appa- '2,957,816Patented Oct. 25, 1960 ratus shown in Fig. 1 and indicates otherfeatures of the subject electrolytic cell.

Figs. 3 and 4 are side elevational Views of the carriage? bearingassembly for raising the upper cell portion.

Referring now to the drawings, to show clearly the position of O-ringseals which make possible the con-V tinuous exchange cathodes, the lowercell assembly, cornprising the cell, is shown from the top in Fig. l andthe upper assembly, which permits cathode exchange, is shown from thebottom. This assembly consists of a water-cooled gas-tight chamber 1containing a graphite crucible 2 which serves as the anode. A plate 3 ofconducting material may be pressed against the bottom of the Crucible 2to make electrical contact.

surrounding the entrance to the chamber and extending outward, a tablemember 6 with a smoothly-nished sur- 6. An oval O-ring 10 composed ofsynthetic plastic,`

such as polyethylene, resistant to cell eluents, encircles the twoopenings of the cathode chambers 8a and 8b and is depressed by theweight of the upper assembly so as to seal the combined cathode and cellchambers effectively from the atmosphere. n

Assuming the position of the apparatus as indicated in Fig. l, the loweropening o-f cathodechamber 8a is in' vertical alignment with the cellopening, around which a secondary O-ring 11 is secured. This additionalseal supplements O-ring 10 in actual operation but has an a even moreimportant function in maintaining an independent seal between cathodechambers 8a and 8b when one is opened to the atmosphere for removal ofthe metal from the deposition cathode tip.

The cathode 12a in central alignment Wit-h the Walls of the chamber 8acan be lowered through the opening in the lid 13 Aand is assisted inremaining truly vertical by a seal 14 as the cathode tip is submerged inthe electrolyte in the Crucible 2, thus completing the electricalcircuit.

Unexpectedly, it w-as observed that a conical tip cathode was notattacked by gas evolved from the anodic bottom of the cell. For bestresults it was found that the distance o-f the tip of the cathode fromthe bottom of the anodic Crucible should be greater than the spacebetweenthe cathode andthe crucible wall. When these clearances `aremaintained, preferential growth of the deposit on the tip of the cathodeand subsequent shorting out ofthe D.C. circuit `between the cathode andthe Crucible bottom are prevented. The cathode construction ispreferably of cold rolled A nickel and that portionof the shaftimmediately above the conical tip may be protected from cell gas by `asimple carbon or graphite sleeve. The cathodes are further preferablyprotected by air-cooling means as indicated by the `arrows at the top ofcathode 12a in Fig. 1. Y

Picturedin Figs. 3 and 4 are the quick-acting clamps andcarriage-bearing assembly for raising the upper cell portion. The toggleclamp 15, when depressed, lowers the shaft 16 so that the Wheel 17presseson the table 6 and raises the carriage 9. When the section isthus lifted, the holding lug 17a is also released and the entireassembly may be easily shifted, so that chamber 8b lies in verticalalignment with the cell opening. Clearance between carriage 9 and table6 is so adjusted that O-rings 11 and 12 are partially compressed evenwhile carriage 9 is in the raised position. -A gas-tight seal may thusbe The crucible.' 2 is surrounded by -a heating system 4 and isinsulated, f from the chamber 1 by refractory material 5. Completely vmaintained at all times. Release of the clamps compresses the ovalO-ring seals 10and 11, and immediate lowering of cathode 12b allowscontinuation of the reactive metal deposition.v This procedure permitspractically continuous electrolysis, since the'deposited material on thetip of the cathode 12a now has ample time to cool, and is subsequentlyremoved,v through the'lid 13. The cathode chamber 8a is evacuated and.is then ready for reuse as soon as the cathode 12b, which isat that timebeing employed, requires removal of deposited metal.

As will be noted in both Figs. l and 2, the Olrings 10 and =11 aresituated in a manner that will preventV conflict withv each other whenthe exchange of cathode chambers is effected. During this movement, whenneither chambers 8a or 8b are resting on O-ring 11, both'chambers are inevacuated or inert gas-filled condition'. An alter'- nate method forproviding a workable, positive seal means is to place a sheet ofpolyethylene or other suitable plastic between the sliding carriage andthe table. Such material acts as an infinite number of O-rings andallows the cathode chambers to be Sealed in any position.

Another effective method for maintaining a gas-tight seal without theuse of an oval-ring is possible. This may be done by providing multiplerings similar to O-ring 11l along the surface of table 6. These ringsshould be spaced at intervals equal to the distance between cham bers 8aand y8b so that the bottom opening of each suchl chamber will beencircled by such a ringy during operation. Any number of rings may beso provided to correspond with any desired number of cathode chambers.

The entire procedure for shifting cathodes takes but a moment and isextremely simple, inexpensive, compatible with maintaining the purity ofthe metal depositedl on the cathode and makes possible a practicallycontinuous operation. The salt bath, or electrolyte, is under constantprotection from air and moisture, and the temperature within the cell isalways sufficiently high to prevent its solidification, especiallyduring cathode changes.

In preparing for actual operation of the apparatus of the invention, afused electrolytic salt mixture is fed into the cell. Suitableelectrolytes containing alkali metal halides and alkaline earth metalhalides, and a chloride of the desired reactive metal are disclosed andclaimed in the copending application of R. M. Sarla, Serial No. S12,297, filed May 3l, 1955. The upper'and lower assemblies are alignedin secure position with the 0rings depressed to exclude the atmosphere.The cathode of the chamber in use is held in readiness to be loweredinto the electrolyte. Referring now to Fig. 2, the cell is evacuatedthrough an outlet 1-8 to approximately 100 microns after which thechamber and cell may be flooded with an inert gas, such as argon,through the inlet 19. or the operation may proceed under pressures belowatmospheric. The temperature within the cell is now elevated to melt thesalt and when fusion is complete, the refractory metal halide, which maybe gas, liquid or solid, is fed in and combined with the fused salt baththrough the opening to form the electrolyte. All is now in readiness forsubmergence of the cathode into the electrolyte for completion of theelectrolysis vcircuit and for deposition vof the pure reactive metal onthe cathode tip. The halogen gas which is evolved at the anode rises tofill the area above the electrolyte and is either eliminated by suctionthrough `the outlet 21 or by cycling the inert gas.

To offset the possibility of corrosive action by the halogen gas at theelevated temperature within the cell, a series of inlets, hollows, andoutlets honeycomb the apparatus for circulation of water for coolingvarious'portions of the equipment independently of each other. Fig. 2illustrates the sectionsof the apparatus'which are so cooled, and theseinclude, progressing fromthe lower portion to the upper, the anode,shell, under-portion of the table, cathode chamber, cathode chamber lidandthe cathode itself. By so cooling the entire assembly, not only isthe corrosive action of the evolved gas negated, but the seals areprotected from burning, or even losing. their resiliency.

It is to be understood thata number of modifications may be made in theapparatus of the invention without departing from the spirit thereof.For example, the anode and cathode chambers may be of any desiredconfiguration which would assist in the electrolysis and collection ofthe end metallicproduct. While the anode chamber as shown is externallyheated, it would also be quite` feasible to heat said chamberinternally,as by heating elements inserted in the crucible.

Subject matter particularly related'to the'electroly'tic mixturessuitable for use in conjunction with the previously described cell isdisclosed and claimed in my copending application Serial No. 512,297,filed May 31. 1955.

'Ihis application is a continuation-impart of application Serial No.631,185, filed December 28,' 1956, now aban-A doned, by R. M. Sarla,entitled ApparatusforProducing Tantalum, and application Serial No.631,186, filed" December 28, 1956, now abandoned, by R. M. S'arla" andE. O. Schneidersmann, entitled Apparatus for'Fus'on Electrolysis ofReactive Metals.

What is claimed is:

l. In an electrolytic cell for the production ofhigh melting pointreactive metals of groups IV, V and VI of(y the periodic table by thedeposition thereof` from an" electrolytic bath, the combinationcomprising a lower cell assembly consisting of a water-cooled chambercontaining a crucible serving as the cell anode, heatingm'eans forheating the contentsv of said Crucible,l a table member surrounding theopening to saidchamb'er at the upper" removably mounted therein; sealingmeans between said' assemblies; means for supplying electriccurrentto'said' anode and cathode; feeding means for introducing anelectrolytic charge into said cell; and means for evacuating and forinjecting inert gas in said cell andV cath'o'd'e' chamber.

2. The cell of claim 1 whereinrefractory material is' provided betweensaid vacuum chamber and crucible for' insulation. Y

3. The cell of claim l wherein plastic O-rin'gs' encircle the openingsof the cathode chambers, and of the vacuum' chamber to provide aneffective seal again'st'the atmos` phere.

4. The cell of claim l wherein plastic O-rings encircle` the opening ofthe anode chamber and are intervallicly spaced along said table memberto seal each oflsaid cathode chambers.

5. The cell of claim 2 wherein the distance from`th'e tip ofV saidcathode tothe bottom of saidcmcible is` greater than the distance fromsaid cathode to the wall of said Crucible.

6. In an electrolytic cell for the production vof high melting pointreactive metals of groups IV, V and VI of the periodic table, said cellhaving an inlet for receiving a cathode therein, a cell cover assemblyto provide for substantially continuous production of metal whichvcomprises a table member fitted to the top of said'ell and having anopening to permit .the passage of a cath` ode therethrough into saidcell, a base member movably mounted upon said table member, a plurality`of chambers adapted to contain cathodes fixedly' and sealably mountedon said base member,v said' chambers" having lower outlets thereinextending through said base member .to permit asaid cathode to belowered into said cell upon moving said kbase member on saidtablejmember t9 align a said chamber with said cell, annular' sealv 5 6ing means fixed to the lower surface of said base memcontinuouslysealing said chambers and said cell from ber to surround said chamberoutlets and to compressibly the atmosphere. and continuously contact theupper surface of said table v References Cited in the me of this patentmember, said base member and affixed sealing means arranged upon saidtable member to be movable thereon 6 UNITED STATES PATENTS to permitalternate alignment of said chambers with said 1,838,666 Fink et al.Dec. 29, 1931 cell and alternate employment of cathodes therein while2,760,930 Alpert et al. Aug. 28, 1956

1. IN AN ELECTROLYTIC CELL FOR THE PRODUCTION OF HIGH MELTING POINTREACTIVE METALS OF GROUPS IV, V AND VI OF THE PERIODIC TABLE BY THEDEPOSITION THEREOF FROM AN ELECTROLYTIC BATH, THE COMBINATION COMPRISINGA LOWER CELL ASSEMBLY CONSISTING OF A WATER-COOLED CHAMBER CONTAINING ACRUCIBLE SERVING AS THE CELL ANODE, HEATING MEANS FOR HEATING THECONTENTS OF SAID CRUCIBLE, A TABLE MEMBER SURROUNDING THE OPENING TOSAID CHAMBER AT THE UPPER PORTION THEREOF, AND EXTENDING OUTWARDLYTHEREFROM, AN UPPER CELL ASSEMBLY COMPRISING A PLURALITY OF WATER-COOLEDCATHODE CHAMBERS SECURED TO A BASE WHEELED CARRIAGE SLIDABLY MOUNTED ONSAID TABLE MEMBER TO PERMIT SUCCESSIVE IMMERSION IN ELECTROLYTE OFDEPOSITION CATHODES REMOVABLY MOUNTED THEREIN, SEALING ELECTRIC CURRENTTO SAID ASSEMBLIES, MEANS FOR SUPPLYING ELECTRIC CURRENT TO SAID ANODEAND CATHODE, FEEDING MEANS FOR INTRODUING AN ELECTROLYTIC CHARGE INTOSAID CELL, AND MEANS FOR EVACUATING AND FOR INJECTING INERT GAS IN SAIDCELL AND CATHODE CHAMBER.